docstr: Reduces the tensor data across all parties.
docstr_tok: ["Reduces","the","tensor","data","across","all","parties","."]
code: def reduce(self, tensor, dst, op=ReduceOp.SUM, async_op=False):
      """Reduces the tensor data across all parties."""
      tensors = self.gather(tensor, dst)
      if self.rank == dst:
          reduce_fn = self._reduce_op_to_function(op)
          return reduce_fn(torch.stack(tensors), dim=0)
  
imports: import logging
  import threading
  from operator import itemgetter
  from queue import Queue
  import torch
  from torch.distributed import ReduceOp
  from .communicator import Communicator
label_desc: Use image node_id 10 for calling the InProcessCommunicator obj's underlying member method code with example usage: obj.reduce(tensor, dst, op, async_op) and returns: reduce_fn